import threading
import time

my_list = []

def write_data():
    for i in range(3):
        my_list.append(i)
        print('add: ',i)
    print(my_list)

def read_data():
    print(my_list)

if __name__ == '__main__':
    write_thread = threading.Thread(target=write_data)
    read_thread = threading.Thread(target=read_data)

    write_thread.start()
    time.sleep(1)
    read_thread.start()